1. Field of the Invention
The present invention relates to an internal combustion engine having a laser ignition device for direct gasoline injection, and to a method for operating such an engine.
2. Description of the Prior Art
Internal combustion engines for direct gasoline injection are known in various designs from the prior art. Such engines are lately used more and more, since they have lower fuel consumption and low emissions. A common feature of the known engines is that they typically have an injection valve in a central position and a spark plug disposed in such a way that they are located on a periphery of the spray of fuel injected into the combustion chamber. The ignition of the fuel, which propagates essentially conically from the injection valve, is effected at the periphery of the cone, since only there is an ignitable fuel-air mixture present. In practice, however, in positioning the spark site of the spark plug, problems arise in positioning this spark site precisely in the narrow peripheral zone in the region of the ignitable fuel-air mixture. This is due on the one hand to component tolerances of the injection valve, spark plug, and cylinder head, and on the other to the deviation in the spray geometry from one cycle to another, and thus the ignitable peripheral zone can vary to a certain extent. Cyclical deviations in the spark site within the electrode region can also occur in the spark plug, and the spray geometry can vary from aging because of deposits or as a function of the engine performance graph. These factors lead to reduced efficiency on the one hand and to problems with the exhaust gases on the other.
Moreover, it has lately been proposed that the conventional spark plug be replaced by a laser ignition device, with ignition again taking place at the periphery of an injected fuel vapor cloud.